C9- Transport in Plants

Question 1

Why do plants need a transport system

4

Answer 1

High metabolic demands in areas of plant without glucose- glucose must be transported from source to sink to be used for aerobic respiration

Hormones and mineral ions needed across plant

size- transport systems needed to bridge distances between roots and leaves

SA:V- cannot rely on simple diffusion alone to meet metabolic demands of the plant

Question 2

What is a vascular bundle

Answer 2

The transport system in plants, made up of the phloem and the xylem

Question 3

Monocot vs Dicot

Leaf ventillation

Answer 3

Monocot- parallel

Dicot- feathered and palmate leaf

Question 4

Monocot vs Dicot

vascular bundles

Answer 4

Monocot- vascular bundles are random

Dicot- Vascular bundles in a ring

phloem on outer ring, xylem on inner ring

Question 5

Monocot vs Dicot

Flowers

Answer 5

Monocots- Sepals, petals, anthers always come in multiples of 3

Dicots- Sepals, petals and anthers never come in multiples of 3

Question 6

Monocot vs Dicot

Roots

Answer 6

Monocot- fibrous roots with many branches

Dicot- Tap root with fibrous roots attached

Question 7

Tree girdling

Answer 7

Remove outer layer of bark, severing the phloem, preventing translocation

kills tree efficiently

Scars forms and tree bulges just above due top build-up of sap and movement of water by osmosis

Question 8

Shape of xylem and phloem in dicots roots

Answer 8

X xylem

0 in each quadrant of X are phloem

Question 9

Xylem function

Answer 9

Transports water and dissolved minerals upwards from the soil (roots) to the aerial parts (stems and leaves) of the plant by the process of transpiration

Xylem also provides structural support.

Question 10

Phloem function

Answer 10

Transports soluble organic substances (sucrose) throughout the plant by translocation – from where they are produced (source) to where they are used (sink)

Question 11

Xylem structure

5

Answer 11

Spirals of lignin so tube does not collapse under transpiration pull and waterproof

Non lignified pits allow lateral movement of water between vessels and cells

parenchyma- stores food, also has tannin which is bitter to deter attack by insects

Narrow- increases adhesion, aiding upwards movement of water by capillary action

one way flow

Question 12

Phloem structure

4

Answer 12

two way flow

sieve tube elements joined end to end

living cells- cytoplasm of tube element connected to companion cell

Companion cell has many mitochondria to produce ATP for active transport

Question 13

Three types of cells found in phloem tissue

Answer 13

sieve tube element

companion cell

parenchyma

Question 14

How does structure of xylem differ form cell walls in typical plant cells

Answer 14

Thicker

Lignified

Contains pits

Question 15

Moss have no vascular tissue

Why may this effect the size it can grow

Answer 15

No support from vascular tissues

remains small

maintains short diffusion pathway and large SA:V

Question 16

transpiration vs transpiration stream

Answer 16

Transpiration is the evaporation of water form the leaves and the transpiration stream is the movement of water form the roots to the the rest of the plant through the xylem

Question 17

Transpiration stream mechanism

6

Answer 17

water evaporates from mesophyll cells, lowering their water potential

water moves out of xylem into the cells by osmosis

Water molecules form H bond with the carbohydrates in the walls of the xylem- adhesion

form H bonds between molecules- cohesion

This pull water up in a continuous column- the transpiration pull

results in tension in xylem aiding the movement of water into the roots

Question 18

Evidence for cohesion tension theory in plants and trees

Answer 18

when xylem vessels are broken air is drawn in and not water leaking out

When a xylem is broken, a plant cannot move water up the vessel as the continuous stream is broken

in day, diameter of tree trunk shrinks, tension in xylem pulls it in

Question 19

Factors affecting transpiration

light intensity

Answer 19

increasing light intensity increases the number of open stomata

increasing the rate of loss of water vapour

Question 20

Factors affecting transpiration

relative humidity

Answer 20

Total amount of water in the air compare to the total amount of water that the air can hold

affect concentration gradient for water

Question 21

Factors affecting transpiration

Temperature- 2 ways

Answer 21

increases kinetic energy of water molecules so they evaporate more readliy

increased temperatures mean air can hold more water, shallowing the concentration gradient

Question 22

Factors affecting transpiration

Air movement

Answer 22

affects concentration gradient for water vapour to diffuse out of the leaf

Question 23

Factors affecting transpiration

soil water availability

Answer 23

if very low the plant will be under stress and transpiration rates will be very low

Question 24

Using the term water potential can you explain how water might continue to move into the root hair cell

Answer 24

Cells have a higher concentration of minerals and sugars so will have a LOWER WATER POTENTIAL

Soil has very low levels of dissolved minerals so will have a HIGH WATER POTENTIAL

Water will therefore move INTO the cells from a high water potential to a low water potential

Question 25

Plasmodesmata define

Answer 25

Microscopic canals that passes through adjacent plant cell walls allows direct communication of molecules between adjacent cells

Question 26

Symplast pathway

Answer 26

Symplast = cytoplasm All cells are connected through plasmodesmata Water moves through the connecting cytoplasm Water will move from a high water potential to a lower water potential

Question 27

Why is the apoplast pathway 'faster' than the symplast pathway?

Answer 27

In the apoplast pathway, water forms hydrogen bonds with surrounding molecules, and walls cohesion and adhesion

Question 28

Apoplast pathway

Answer 28

Apoplast = cell wall Water also moves through the connecting cell walls Cohesion and adhesion allows a continuous flow of water through these fibres The pull from the xylem causes a continuous flow

Question 29

The casparian strip

Answer 29

The casparian strip is waxy and BLOCKS the flow of water through the cell walls Water is therefore forced back into the symplast pathway from the apoplast pathway

Question 30

How are root hair cells adapted to their function 4

Answer 30

Microscopic size means they can penetrate between soil particles Many root hair cells with large SA:V Each cell has a short diffusion pathway Many mitochondria to provide ATP for active transport

Question 31

Movement of water into the xylem

Answer 31

water moves across root through both apoplast and symplast pathways until it reaches endodermis (layer of cells surrounding vascular tissue) meets the casparian strip apoplast pathway forced into the cell joining the symplast pathway must pass through selectively permeable membrane- moves potentially toxic residues

Question 32

Evidence for the role of active transport in root pressure

Answer 32

root pressure disappears when plant given cyanide, Cyanide stops ATP production so no active transport so no root pressure if levels of respiratory substrates fall, so does root pressure root pressure increases with rise in temperature, so a chemical reaction must be involved

Question 33

Root pressure

Answer 33

active pumping of mineral ions in to the xylem from the endodermis cells to alter water potential and move water by osmosis independent of transpiration gives water a push up the xylem

Question 34

how does water move from the xylem to the root hair cells

Answer 34

the symplastic and apoplastic pathways

Question 35

How does water move from xylem to cells and then transpiration

Answer 35

water moves into spongy mesophyll and then evaporates into surrounding air spaces leaves via apoplastic pathways as water evaporates water potential maintains the transpiration stream

Question 36

what type of process is the controlling of the size of the stomata opening

Answer 36

turgour driven process

Question 37

Describe the process of the controlling the size of guard cell openings

Answer 37

Low turgor the asymmetric configuration of the guard cell walls causes it to close When environmental conditions are favourable the guard cell pumps in solutes by active transport increasing turgor Cellulose hoops prevent expansion, inner wall less flexible then outer wall cause the stomata to become bean shaped

Question 38

What is the source and sink in a plant

Answer 38

Source- origin of glucose Sink- Destination of glucose

Question 39

What is an assimilate in plant transport

Answer 39

general term for what is being transported through the phloem

Question 40

Why is sucrose transported in pant and not glucose

Answer 40

Less metabolically active also soluble less likely to be used up for respiration while being transported

Question 41

Translocation Apoplast pathway from source to phloem vessel

Answer 41

Sucrose is moved into the cytoplasm across the cell membrane – this process is ACTIVE moves by co transport across cell membrane form the cell wall to cytoplasm to join the simplastic pathway

Question 42

Translocation Symplast pathway from source to phloem vessel

Answer 42

Sucrose is moves through the cytoplasm and plasmodesmata Passive process- diffusion only

Question 43

Cotransport of sucrose from apoplast to symplast pathway mechanism

Answer 43

protons leave membrane by a proton pump then re-enter the membrane down the sucrose concentration gradient with a molecule of sucrose in a co transporter

Question 44

Why does water move from xylem to phloem in translocation

Answer 44

As there is a large amount of sucrose in the phloem it will have a LOW water potential. Water will therefore move from the xylem (which has a higher water potential)

Question 45

Does water move by osmosis or diffusion from the xylem to the phloem

Answer 45

water diffuses as it leaves non lignified pits and then the plasmodesmata so never crosses a membrane

Question 46

Where does movement in the phloem originate from

Answer 46

As water moves in it will increase the hydrostatic pressure – and force movement in the phloem IN BOTH DIRECTIONS

Question 47

Translocation Unloading

Answer 47

The sucrose unloads where it is required and will simply diffuse down a concentration gradient. The sucrose is quickly converted to glucose (used in respiration) or starch (storage) so that the concentration gradient is maintained

Question 48

Evidence for the mass flow hypothesis

Answer 48

Advances in microscopy allow us to look at the companion cells- many mitochondria so must be active If use cyanide to poison the companion cell translocation stops flow is around 10 000 times faster than diffusion so there must eb an active process involved

Question 49

Ion that is involved in the cotransport of the loading of the phloem

Answer 49

H+ (proton)

Question 50

Xerophytes general classification

Answer 50

Plants that live in dry habitats and have adaptations to conserve their water enables them to live and reproduce in areas with low water availability

Question 51

Hydrophytes general classification

Answer 51

plants that live in water have and need adaptations to cope with growing in water or permanently saturated soil if water logged the air spaces fill with water and not air

Question 52

4 key xerophyte adaptations and what they do

Answer 52

Thick waxy cuticle- reduce water loss by transpiration sunken stomata and hairy leaves- maintain a humid and still microclimate reducing concentration gradient leaf loss- loose leaves when water not available, trunk turns green to photosynthesise root adaptations- long deep tap rots or wide shallow roots to increase access to water

Question 53

5 Hydrophyte adaptations and what they do

Answer 53

Stomata on upper side of leaves and always open- maximum gas exchange, water loss is ok as much more available, on upper side so exposed to air wide flat leaves- capture as much light as possible for photosynthesis no waxy cuticle- no need to conserve water as plenty is available air sacs- To allow plant to float to the surface of the water small roots- water can diffuse directly into stem and leaf tissue

Question 54

Potometer method

Answer 54

airtight potometer dry leaves and cut stalk at a slant underwater measure time taken for air bubble to travel a known distance calculate volume of water uptake maintain constant conditions